The invention relates to a remote control system comprising a transmitter and a receiver, the transmitter comprising generating means for generating a message consisting of a series of bits, the first of which is a start bit having a predetermined value, an encoding circuit for converting each bit of the message into a biphase bit having a predetermined bit period which comprises a first and a second bit interval and whose logic value is represented by the presence of a pulse in the first or the second bit interval, means for transmitting a biphase signal thus obtained to the receiver, and the receiver comprising means for receiving the transmitted biphase signal, a decoding circuit for decoding the start bit, starting in response thereto a periodical reference signal whose period corresponds to the predetermined bit period, and for regaining the message. The invention also relates to a transmitter and a receiver suitable for use in such a remote control system.
A remote control system of the type described in the opening paragraph is constituted, for example, by the integrated circuits SAA3006 and SAA3028 from the Firm of Philips, which circuits are described in "Data Handbook IC02a of Philips Electronic Components and Materials, 1988". Such a remote control system is used for the wireless transmission of operating commands from a remote control unit to an apparatus to be operated by means of, for example, infrared light. In the known remote control systems each message comprises two start bits, one control bit, five address bits and six command bits. The address bits indicate for which apparatus (for example television receiver or video recorder) the message is intended. The command bits indicate the function to be operated on the apparatus mentioned. The control bit indicates whether the message comprises a command other than the foregoing or whether it forms part of a series of repeatedly transmitted identical messages.
Complicated commands frequently consist of a plurality of sub-commands. For example, the video recorder command "record the television program on channel 31 from 20.15 hours to 21.45 hours on 22 July" comprises a sub-command "timer" and a plurality of further sub-commands each comprising a number for the start and stop time, date and channel. The transmitter is often adapted in such a way that the command to be transmitted is first composed on the remote control unit, checked for consistency with a predetermined protocol and only sent after a transmission key has been energized.
In the known remote control system each sub-command is transmitted as a separate message. However, this is not economical because each message comprises the start bits and the control bit, as well as the address bits for addressing the same video recorder. Moreover, there is a risk that short interruptions of the infrared light may lead to erroneous reactions of the receiving apparatus. For example, if the message with the sub-command "timer" is not received, the sub-commands in the subsequent messages are interpreted erroneously, for example as instructions for tuning to a new channel number.